1. Field of the Invention
The present invention relates to a vehicle engine output control apparatus adopted when an engine output of a vehicle is controlled to a target engine output.
2. Description of the Related Art
A traction control apparatus is well known as one of control apparatus which control an engine output of a vehicle. In the traction control apparatus, when an acceleration slip of the driving wheels is detected, a slip rate S is controlled to cause a coefficient .mu. of friction between the wheels and a road surface to fall within a maximum range (a hatched range in FIG. 18). The slip rate S is given by (VF-VB/VF).multidot.100 (%), where VF is the wheel velocity of driving wheels, and VB is the vehicle velocity. More specifically, when a slip of driving wheels is detected, an engine output is controlled to cause the slip rate S to fall within the hatched range, thereby controlling the coefficient .mu. of friction between wheels and a road surface to fall within the maximum range. Thus, an acceleration slip of driving wheels is prevented to improve acceleration characteristics of a vehicle.
In general, it is known that to control engine output (torque) of a vehicle, a throttle valve provided in an intake pipe is controlled to adjust amounts of intake air and fuel supplied to cylinders.
Thus, heretofore, there has been proposed a method in which a target value of engine torque is set in accordance with driving condition of the vehicle, and opening of the throttle valve is controlled so that an intake air amount for the target engine torque is obtained. In this case, an actual intake air amount is measured by an air flow sensor, and the throttle valve opening is feedback controlled in dependence on a difference from the target intake air amount.
Since, however, in the above engine torque control system, an actual intake air amount measured by the air flow sensor is fed back to control the opening of the throttle valve in dependence on a difference from the target intake air amount, the engine torque may become uncontrollable if a malfunction occurs in the air flow sensor.